Using general-relativistic hydrodynamical simulations, we show that merging binary neutron stars can form hypermassive neutrons stars that undergo the one-arm spiral instability. We study the particular case of a dynamical capture merger where the stars have a small spin, as may arise in globular clusters, and focus on an equal-mass scenario where the spins are aligned with the orbital angular momentum. We find that this instability develops when postmerger fluid vortices lead to the generation of a toroidal remnant—a configuration whose maximum density occurs in a ring around the center-of-mass—with high vorticity along its rotation axis. The instability quickly saturates on a time scale of $\sim 10\mathrm{ms}$, with the $m=1$ azimuthal density multipole mode dominating over higher modes. The instability also leaves a characteristic imprint on the postmerger gravitational wave signal that could be detectable if the instability persists in long-lived remnants.

We consider models of chaotic inflation driven by the real parts of a conjugate pair of Higgs superfields involved in the spontaneous breaking of a grand unification symmetry at a scale assuming its supersymmetric value. We combine a superpotential, which is uniquely determined by applying a continuous $R$ symmetry, with a class of logarithmic or semilogarithmic Kähler potentials which exhibit a prominent shift symmetry with a tiny violation, whose strengths are quantified by $c_{-}$ and $c_{+}$. The inflationary observables provide an excellent match to the recent BICEP2/Keck Array and Planck results, setting $3.5\times {10}^{-3}\lesssim r_{\pm }=c_{+}/c_{-}\lesssim 1/N$, where $N=3$ or 2 is the prefactor of the logarithm. Inflation can be attained for sub-Planckian inflaton values, with the corresponding effective theories retaining the perturbative unitarity up to the Planck scale.

We comparatively analyze the rare ${\mathrm{\Lambda }}_b\to \mathrm{\Lambda }{\ell }^{+}{\ell }^{-}$ channel in the standard model, supersymmetry, and Randall-Sundrum model with custodial protection (${\mathrm{RS}}_c$). Using the parametrization of the matrix elements entering the low-energy effective Hamiltonian in terms of form factors, we calculate the corresponding differential decay width and lepton forward-backward asymmetry in these models. We compare the results obtained with the most recent data from LHCb as well as lattice QCD results on the considered quantities. It is obtained that the standard model, with the form factors calculated in light-cone QCD sum rules, cannot reproduce some experimental data on the physical quantities under consideration, but the supersymmetry model can do it. The ${\mathrm{RS}}_c$ model predictions are roughly the same as the standard model, and there are no considerable differences between the predictions of these two models. In the case of differential decay rate, the data in the range $4{\mathrm{GeV}}^2/{\mathrm{c}}^4\le q^2\le 6{\mathrm{GeV}}^2/{\mathrm{c}}^4$ cannot be described by any of the considered models.

We examine the prospects for detecting light charged Higgsinos that are expected to be a necessary feature of natural supersymmetry (SUSY) models via $pp\to {\tilde{W}}_1^{\pm }{\tilde{W}}_1^{\pm }jj+X$ processes arising dominantly from $W^{\pm }{W}^{\pm }$ fusion at LHC13. The signal will be a pair of same-sign leptons ($e$ or $\mu$) in events with two relatively forward, hemispherically separated jets with a large rapidity gap. We find that even though the Higgsinos have a full-strength $SU(2)$ gauge couplings to $W$ bosons, the LHC13 cross section for the production of same-sign Higgsino pairs is smaller than 0.02 fb over most of the interesting range of natural SUSY parameters, even before leptonic branching fractions of the chargino are included. This cross section is strongly suppressed because the two neutral Majorana Higgsinos can be combined into a single Dirac neutralino if the bino and the winos are much heavier than the Higgsinos, as is the case in natural SUSY models: in this limit, Higgsino couplings to $W$ bosons exhibit an emergent (approximate) $U(1{)}_{\text{ino}}$ global symmetry that suppresses same-sign Higgsino production by vector boson fusion. We conclude that this channel is not a viable way to search for natural SUSY even at the high luminosity upgrade of the Large Hadron Collider.

The CMS $e^{+}{e}^{-}jj$ events of invariant mass near 2 TeV are consistent with a $W^{\prime }$ boson decaying into an electron and a right-handed neutrino whose TeV-scale mass is of the Dirac type. We show that the Dirac partner of the right-handed electron neutrino can be the right-handed tau neutrino. A prediction of this model is that the sum of the ${\tau }^{+}{e}^{+}jj$ and ${\tau }^{-}{e}^{-}jj$ signal cross sections equals twice that for $e^{+}{e}^{-}jj$. The Standard Model neutrinos acquire Majorana masses and mixings compatible with neutrino oscillation data.

The spin decomposition of the proton is a long-standing topic of much interest in hadronic physics. Lattice QCD has had much success in calculating the connected contributions to the quark spin. However complete calculations, which necessarily involve gluonic and strange-quark contributions, still present some challenges. These “disconnected” contributions typically involve small signals hidden against large statistical backgrounds and rely on computationally intensive stochastic techniques. In this work we demonstrate how a Feynman-Hellmann approach may be used to calculate such quantities, by measuring shifts in the proton energy arising from modifications to the QCD action. We find a statistically significant nonzero result for the disconnected quark spin contribution to the proton of about $-5\%$ at a pion mass of 470 MeV.

We study the mixing of the scalar glueball into the isosinglet mesons $f_0(1370)$, $f_0(1500)$, and $f_0(1710)$ to describe the two-body decays to pseudoscalars. We use an effective Hamiltonian and employ the two-angle mixing scheme for $\eta$ and ${\eta }^{\prime }$. In this framework, we analyze existing data and look forward to new data into $\eta$ and ${\eta }^{\prime }$ channels. For now, the $f_0(1710)$ has the largest glueball component and a sizable branching ratio into $\eta {\eta }^{\prime }$, testable at BESIII.

A confining, symmetry-preserving, Dyson-Schwinger equation treatment of a vector $\otimes$ vector contact interaction is used to formulate Faddeev equations for the nucleon and $\mathrm{\Delta }$-baryon in which the kernel involves dynamical dressed-quark exchange and whose solutions therefore provide momentum-dependent Faddeev amplitudes. These solutions are compared with those obtained in the static approximation and with a QCD-kindred formulation of the Faddeev kernel. They are also used to compute a range of nucleon properties, amongst them: the proton’s $\sigma$-term; the large Bjorken-$x$ values of separate ratios of unpolarized and longitudinally polarized valence $u$- and $d$-quark parton distribution functions; and the proton’s tensor charges, which enable one to directly determine the effect of dressed-quark electric dipole moments (EDMs) on neutron and proton EDMs.

We calculate the $T$ matrices of kaon-nucleon ($KN$) and antikaon-nucleon ($\overline{K}N$) scattering to one-loop order in SU(3) heavy baryon chiral perturbation theory ($\mathrm{HB}\chi \mathrm{PT}$). The low-energy constants (LECs) and their combinations are then determined by fitting the phase shifts of $KN$ scattering and the corresponding data. This leads to a good description of the phase shifts below 200 MeV kaon laboratory momentum. We obtain the LEC uncertainties through statistical regression analysis and successfully reduce one parameter. We also determine the LECs through the use of scattering lengths in order to check the consistency of the $\mathrm{HB}\chi \mathrm{PT}$ framework for different observables and obtain a consistent result. By using these LECs, we predict the $\overline{K}N$ elastic scattering phase shifts and obtain reasonable results. The scattering lengths are also predicted, which turn out to be in good agreement with the empirical values except for the isospin-0 $\overline{K}N$ scattering length that is strongly affected by the $\mathrm{\Lambda }(1405)$ resonance. As most calculations in the chiral perturbation theory, the convergence issue is discussed in detail. Our calculations provide a possibility to investigate the baryon-baryon interaction in $\mathrm{HB}\chi \mathrm{PT}$.

In this paper we obtain an analytical solution of the relativistic Boltzmann equation under the relaxation time approximation that describes the out-of-equilibrium dynamics of a radially expanding massless gas. This solution is found by mapping this expanding system in flat spacetime to a static flow in the curved spacetime ${\mathrm{AdS}}_2\otimes {\mathrm{S}}_2$. We further derive explicit analytic expressions for the momentum dependence of the single-particle distribution function as well as for the spatial dependence of its moments. We find that this dissipative system has the ability to flow as a perfect fluid even though its entropy density does not match the equilibrium form. The nonequilibrium contribution to the entropy density is shown to be due to higher-order scalar moments (which possess no hydrodynamical interpretation) of the Boltzmann equation that can remain out of equilibrium but do not couple to the energy-momentum tensor of the system. Thus, in this system the slowly moving hydrodynamic degrees of freedom can exhibit true perfect fluidity while being totally decoupled from the fast moving, nonhydrodynamical microscopic degrees of freedom that lead to entropy production.

We use the AdS/CFT correspondence and the holographic softwall model to investigate the deep inelastic scattering in the exponentially small-$x$ (Bjorken parameter) regime. We calculate the corresponding structure functions for scalar fields. Using these results, we study the problem of the saturation line in the strong interactions. Our results are consistent with those achieved using other models.

We discuss various aspects of the $O(N)$-model in the vacuum and at finite temperature within the $\mathrm{\Phi }$-derivable expansion scheme to order ${\lambda }^2$. In continuation of an earlier work, we look for a physical parametrization in the $N=4$ case that allows us to accommodate the lightest mesons. Using zero-momentum curvature masses to approximate the physical masses, we find that, in the parameter range where a relatively large sigma mass is obtained, the scale of the Landau pole is lower compared to that obtained in the two-loop truncation. This jeopardizes the insensitivity of the observables to the ultraviolet regulator and could hinder the predictivity of the model. Both in the $N=1$ and $N=4$ cases, we also find that, when approaching the chiral limit, the (iterative) solution to the $\mathrm{\Phi }$-derivable equations is lost in an interval around the would-be transition temperature. In particular, it is not possible to conclude at this order of truncation on the order of the transition in the chiral limit. Because the same issue could be present in other approaches, we investigate it thoroughly by considering a localized version of the $\mathrm{\Phi }$-derivable equations, whose solution displays the same qualitative features, but allows for a more analytical understanding of the problem. In particular, our analysis reveals the existence of unphysical branches of solutions which can coalesce with the physical one at some temperatures, with the effect of opening up a gap in the admissible values for the condensate. Depending on its rate of growth with the temperature, this gap can eventually engulf the physical solution.

The notion that the scalar listed as $f_0(500)$ in the particle data booklet is a pseudo-Nambu-Goldstone (NG) boson of spontaneously broken scale symmetry, explicitly broken by a small departure from an infrared fixed point, is explored in nuclear dynamics. This notion—which puts the scalar (which we shall identify as the “dilaton”) on the same footing as the pseudoscalar pseudo-NG bosons, i.e., octet $\pi$, while providing a simple explanation for the $\mathrm{\Delta }I=1/2$ rule for kaon decay—generalizes the standard chiral perturbation theory ($\chi \mathrm{PT}$) to “scale chiral perturbation theory,” denoted ${\chi \mathrm{PT}}_{\sigma }$, with one infrared mass scale for both symmetries, with the $\sigma$ figuring as a chiral singlet NG mode in the nonstrange sector. Applied to nuclear dynamics, it is seen to provide answers to various hitherto unclarified nuclear phenomena, such as the success of one-boson-exchange potentials, the large cancellation of a strongly attractive scalar potential by a strongly repulsive vector potential in relativistic mean-field theory of nuclear systems and in-medium QCD sum rules, the interplay of the dilaton and the vector meson $\omega$ in dense Skyrmion matter, the Bogomol’nyi-Prasad-Sommerfeld Skyrmion structure of nuclei accounting for small binding energies of medium-heavy nuclei, and the suppression of hyperon degrees of freedom in compact-star matter.

In the current article, the classical analog of the minimal photon sector in the Lorentz-violating Standard-Model extension (SME) is investigated. The analysis is based on describing a photon classically by a geometric ray that satisfies the eikonal equation. The action principle, which leads to the eikonal equation in conventional optics, is demonstrated to work in most (but not all) Lorentz-violating cases as well. Furthermore it is found that the integrands of the action functional correspond to Finsler structures. Based on these results, Lorentz-violating light rays in a weak gravitational background are treated through the use of the minimal-coupling principle. This allows for obtaining sensitivities on Lorentz violation in the photon sector by measurements of light bending at massive bodies such as the Sun. The computations are carried out for the currently running ESA mission GAIA and the planned NASA/ESA mission LATOR. Finally, a range of aspects of explicit Lorentz violation for photons is discussed in the Finsler setting.

We consider a synchrotron radiation from a charged particle moving in a bound orbit around a weakly magnetized Schwarzschild black hole (a static black hole immersed into a constant uniform magnetic field) in its equatorial plane, perpendicular to the magnetic field. In particular, we study the case when the Lorentz force acting on the charged particle is directed outward from the black hole. In this case, for sufficiently large values of the particle’s energy, the particle moves in a nongeodesic bound orbit with loops. Due to a synchrotron radiation, such an orbit decays to a nongeodesic circular stable orbit. We study this transition and calculate the radiated power and energy loss of the particle.

We construct static, spherically symmetric black hole solutions in scalar extended ghost-free massive gravity and show the existence of hairy black holes in this class of extension. While the existence seems to be a generic feature, we focus on the simplest models of this extension and find that asymptotically flat hairy black holes can exist without fine-tuning the theory parameters, unlike the bi-gravity extension, where asymptotical flatness requires fine-tuning in the parameter space. Like the bi-gravity extension, we are unable to obtain asymptotically dS regular black holes in the simplest models considered, but it is possible to obtain asymptotically AdS black holes.

The question is studied of whether an observer can discover quantum gravity in the semiclassical regime. It is shown that it is indeed possible to probe a certain quantum gravity effect by employing an appropriately designed detector. The effect is related to the possibility of having topologically inequivalent geometries in the path-integral approach at the same time. A conformal field theory (CFT) state which is expected to describe the eternal anti–de Sitter (AdS) black hole in the large-$N$ limit is discussed. It is argued under certain assumptions that the black hole boundary should be merely a patch of the entire AdS boundary. This leads then to a conclusion that that CFT state is the ordinary CFT vacuum restricted to that patch. If existent, the bulk CFT operators can behave as the ordinary semiclassical quantum field theory in the large-$N$ limit in the weak sense.

A nonminimally coupled quintessence dark energy in a teleparallel model of gravity is considered. It is clarified how a matter dominated universe with initial negligible dark energy density can evolve to a late time de Sitter space-time via the $Z_2$ symmetry breaking.

We study a class of early dark energy models which has a substantial amount of dark energy in the early epoch of the Universe. We examine the impact of the early dark energy fluctuations on the growth of structure and the cosmic microwave background power spectrum in the linear approximation. Furthermore, we investigate the influence of the interaction between the early dark energy and the dark matter and its effect on the structure growth and cosmic microwave background. We finally constrain the early dark energy model parameters and the coupling between dark sectors by confronting different observations.